1. Field of the Invention
The invention relates to thermoplastic multilayer composites comprising polyamides and polyalkyl (meth)acrylates. The composites have good adhesion between layers.
2. Discussion of the Background
Injection-molded and extruded shaped parts or large-area semi-finished parts such as sheets or profiles made of polyalkyl acrylate or polyalkyl methacrylate (e.g. polymethyl methacrylate (PMMA)) are conventionally used in the production of protective shields for machines, sound--protection walls, coverings for advertizing placards, in bus stops and telephone boxes, in lamp coverings and light domes and many other applications. These composites are used because of their transparency and the good optical properties of the polyalkyl (meth)acrylates, inter alia, the good mechanical property profile, the excellent UV and weathering resistance and also the good processibility of these materials by all customary processing methods.
However, owing to the unsatisfactory chemical resistance and pronounced stress-cracking sensitivity of the polyalkyl (meth)acrylates, the removal of contamination which is not soluble in water or detergents (e.g. so called graffiti) by means of solvent-containing cleaners is generally not possible without impairing the optical properties (clouding, crazing) or even destroying the shaped parts. Because of the unsatisfactory chemical resistance and pronounced stress-cracking sensitivity of the polyalkyl (meth)acrylates, shaped parts made therefrom are not usable wherever the action of solvents or chemicals cannot be definitely ruled out, for example in processing machines, packaging plants, pipe systems or the like.
It would be desirable to rectify this deficiency by coating the shaped parts of polyalkyl (meth)acrylates with a well-adhering material which is transparent or translucent and resistant to chemicals and stress cracking. The coating should here be carried out in an economical manner by the processes customary for thermoplastic processing, such as multicomponent injection molding, coextrusion, pressing, etc. To date, multilayer composites of this type are not known.